Digital Signal Processing in Coherent Optical Communication

Abstract

Over a period of last two decades, fibre optic communication system has evolved from a simple single channel, short distance communication at a data rates of few gigabits per second to multiple channelWavelength Division Multiplexing(WDM) sys- tems operating at as high as 100 Gb/s and beyond over thousands of kilometres. But at higher data rates, linear and nonlinear effects degrades the performance of fiber. Coherent detection technique with advanced digital signal processing is employed to mitigate the linear and nonlinear effects and preservation of full information of the incoming field. In this thesis, modulation techniques suitable for high speed optical communica- tion system is studied. The performance of high speed , long haul optical systems is investigated applying polarized multiplexed modulation formats such as DP-QPSK, DP-16QAM. Extensive Simulation is carried out for the investigation for syatem per- formance compared in terms of distance of transmission link , different launch power and Q-factor. The Digital Signal Processing (DSP) algorithms used for the process are itering for reduction of Chromatic dispersion and by further mitigating cumulative Chro- matic dispersion , Polarization Mode Dispersion with Polarization Demultiplexing us- ing Adaptive Equalization (Blind Equalisation using Constant Modulus Algorithm). Furthermore Carrier Phase estimation is done by using Viterbi-Viterbi algorithm. The comparative study between the modulation formats DP-QPSK, DP-16QAM for two different standard manufacture fiber SSMF (Standard Single Mode Fiber) and LAPSCF (Large Area Pure Silica Core Fiber) are discussed in results .